The first thing I noticed about the picture is on the main character his hands and eye seems like double the pixel width of his feet. That or maybe you just have clusters of pixels there that make it look like that? The player also seems less shaded and detailed than everything else in the scene. (maybe that was intentional, but then the enemies should be the same)
It is pretty hard to tell what he is supposed to represent TBH. An alien with a backpack?
EDIT: I was talking about the red guy in this paragraph. I realized that it might be an enemy and not the player.
The tileset isn't bad, I think that you have too much red and brown going on in the picture though. You can try to add some other colors into it and see if it helps make it look better. (maybe some blues and greys in the tileset bricks?)
The tileset bricks could also probably tile a little better.
I think it needs more variety too! Try to add some more tiles into the tileset. Big bricks that are the size of 4 tiles, pillars, etc.
The enemies right now just look like floaty mines. They don't look bad, just a little generic.
I think you are off to a good start though, I would keep at it!
Ok lol this alien is the player ,actually he looks good in-game with the animations and shooting & stuff. He is an alien with a jetpack and a gun. I will change him to fit the other sprites like you said..
About the tileset tips, I will try that soon and see how its going.
Thanks!